Preservative for plants comprising dipicolinic acid

ABSTRACT

A preservative for plants is described whose active ingredient(s) are the compounds selected from the group consisting of olefin compounds and salts and esters thereof, N-(2-chloro-4-pyridyl)ureas, dipicolinic acid and derivatives and salts thereof, epoxy compounds and salts and esters thereof, and SH-reagents. The preservative is usable for keeping the freshness of plants, in particular fruits, vegetables and cut flowers, and cut flowers for a long period of time.

This is a division, of application Ser. No. 07/831,262, filed Jan. 28,1992, now U.S. Pat. No. 5,171,351, which in turn is a division ofApplication Ser. No. 07/507,332 filed Apr. 10, 1990, currently U.S. Pat.No. 5,112,380.

FIELD OF THE INVENTION

The present invention relates to a preservative for plants, inparticular fruits and vegetables, cut flowers, etc. after beingharvested.

BACKGROUND OF THE INVENTION

Known conventional active ingredient(s) for keeping freshness of fruitsand vegetables after being harvested include, as active ingredient(s)intended for keeping freshness of fruits and vegetables in general, e.g.organic or inorganic germanium (Patent Appln. Disclosure No.293,338/86), biochemical energy source substances, such as sugarphosphate, amino acid phosphate, amidophosphate, hydroxy acid phosphate,adenosine phosphate, guanosine phosphate, creatine phosphate, etc.(JP-A-257,371/87), kojic acid (JP-A-198,372/87), extracts from Chlorellawith hot water, and tocopherol and/or lecithin (JP-A-171,641/87),oligosaccharides (JP-A-214,120/88), vitamin C, salts of vitamin C and/oresters of vitamin C, and gallic acid, or its derivatives(JP-A-22,138/88) and, as active ingredient(s) intended for foodscontaining fruits and vegetables, lysozyme, ascorbic acid, glucose, andglucose oxidase (JP-A-143,672/87), chitin oligosaccharides,N-acetylglucosamine, glucosamine, salts of glucosamine and salts ofchitosan (JP-A-39,569/88), hinokithiol included with cyclodextrin(JP-A-240,765/88), hexose phosphate ferrous salt, or divalent ironcompound and hexose phosphate (JP-A-251,073/88) and, as activeprinciples intended for fruits in general, calcium acetate and calciumlactate and/or sodium acetate (JP-A-143,635/87) and coffee bean cakes(JP-A-133,938/88) and, as active principles intended for strawberry,organic acids, such as malic acid, tartaric acid, etc. and lactose,sucrose, etc. (JP-A-41,255/77) and, as active principles intended forpear, basic amino acids and vitamin C (Japanese Patent Publication No.6,341/80) and, as an active principle intended for pineapple,gibberellin (JP-A-231,944/86).

On the other hand, known active principles for keeping freshness of cutflowers include, e.g. silver thiosulfate, aluminum sulfate,8-hydroxyquinoline sulfate, sugar, etc. (Nosanbutsu Ryutsu GijyutsuNenpo (Annual Report of Distribution Techniques for AgriculturalProducts), pp. 110-112 (1987)) and, as active principles intended forrose, metabolic sugars and phosphonic acids (JP-A-61,401/89), di-ortrivalent basic organic carboxylic acids, and alkali salts thereof(JP-A-131,847/74), kinetin and 6-benzyladenine, which are a substancepossessing a cytokinin activity (Science, 125 650-651, 1957, Plant &Cell Physiology 7 705-706, 1966, Hortscience 8 496-497, 1973),antiseptic/disinfectant (boric acid, chloride of lime, benzoic acid,salicylic acid, sorbic acid, dehydroacetic acid, propionic acid,isocyanuric acid, chlorous acid, hypochlorous acid, paraoxybenzoic acid,and esters thereof, lauryl trimethylammonium-2,4,5-trichloro-carbonilide, tribromosalicylateanilide,3,4,4'-trichlorocarbonilide, hexachlorophene, bithionol, chloramine T,chloramine B halazon, etc.), nitrogen-containing compounds (urea,ammonium sulfate, ammonium chloride, ammonium carbamate, guanidine,alanine, glycine, chlorophyll, sodium nitrilo triacetate, etc.),phosphorus-containing compounds (polyphosphates, such as sodiumtripolyphosphate, potassium pyrophosphate etc., and orthophosphatesalts, such as monobasic sodium, monobasic potassium, monoammonium anddibasic sodium, dibasic potassium, and diammonium hydrogen phosphates,etc.), surface-active agents (anionic, cationic, or nonionicsurface-active agents), inorganic builders (sodium carbonate, potassiumcarbonate, ammonium carbonate, potassium sulfate, etc.), organicbuilders (citric acid, succinic acid, malic acid, tartaric acid, andgluconic acid and sodium salts thereof, pottasium salts thereof,ammonium salts thereof, etc.), solvents (monovalent or polyvalent loweralcohols, such as ethanol, propylene glycol, glycerol, etc.)(JP-A-24,750/74), 2-pyridinethiol-1-oxide (JP-A-98,001/84), ascorbicacid, isoascorbic acid, tryptophan, and thiourea (USP 3,320,046), kojicacid (JP-A-198,372/87), polylysine or its salts (JP-A-169,701/87),gallic acid or its derivatives (JP-A-22,138/88), and coffee bean cakes(JP-A-133,938/88).

At present, as preservatives for cut flowers, there is also customarilyemployed the preservative whose active ingredient(s) is silverthiosulfate. However, the problem of environmental pollution is worried,because silver included in the agents is a heavy metal. In addition,flowers to which the agents are effectively applied are limited to sometypes of flowers, such as carnation. Therefore, recently the developmentof a preservative demonstrating general effects which does not containheavy metals has been desired.

There is known a case where cis-propenylphosphonic acid was employed asa synthetic precursor of phosphomycin which is one of antibiotics (J. ofOrganic Chemistry 35 3510-3512, 1970). In addition, it is a known casethat 2,5-norbornadiene and cis-2-butene which are structural analoguesof the cis-olefin compounds represented by the general formula (I) wereused as materials for the study on plant-aging (Phytochemistry 232765-2768, 1984, PHYSIOLOGIA PLANTARUM 63 114-120, 1985). Thesecompounds are in the form of gas at normal temperature under normalpressure, so that they are not practical.

The N-(2-chloro-4-pyridyl)ureas represented by the general formula (II)were developed as a synthetic plant hormone having a cytokinin activityand are known to show an excellent effect as a plant growth regulator(Patent Publication No. 16,104/82). In the past and present, thesesubstances have been employed as agricultural chemicals for agricultureas well as gardening. Phosphomycin, one of the epoxy compoundsrepresented by the general formula (III), is known in general as anantibiotic (Science, 166, 122, 1969), and already available on themarket.

Dipicolinic acid and its derivatives have been employed as, e.g. aleaf-falling promoter (Patent Publication No. 44,858/73).

The object of the present invention provides preservative which show theexcellent effects on plants after being harvested.

SUMMARY OF THE INVENTION

The present invention relates to a preservative for plants whereinactive ingredient(s) are the compounds selected from the groupconsisting of olefin compounds represented by the general formula (I),or salts or esters thereof: ##STR1## wherein R₁ stands for an alkylgroup having from 1 to 3 carbon atoms, sulfo, phosphono, orhydroxyphenyl group, R₂ stands for a carboxyl, sulfo, phosphono, orhydroxyphenyl group, and n stands for an integer of 0 to 3, and from thegroup consisting of N-(2-chloro-4-pyridyl)ureas represented by thegeneral formula (II): ##STR2## wherein R₃ stands for a hydrogen atom ora lower alkyl group, R₄ stands for an unsubstituted aromatic group, oran aromatic group substituted by a lower alkyl group, lower alkoxy, orhydroxy group or a halogen atom, and X stands for an oxygen or sulfuratom, and from the group consisting of dipicolinic acid, or itsderivatives and salts, and epoxy compounds represented by the generalformula (III), and salts and esters thereof: ##STR3## wherein R₅ standsfor the same as R₁, and R₆ stands for the same as R₂, and SH-reagentsincluding, but not limited to: N-ethylmaleimide, p-chloromercuribenzoicacid, p-chloromercuribenzene sulfonic acid, iodoacetic acid, and5,5'-dithiobis(2-nitrobenzoic acid), etc.

According to the present invention, the freshness of freshly harvestedfruits, vegetables, and portions of plants such as leaves, branches, cutflowers and the like can be maintained for periods of time greater thanheretofore possible by treating the fruits, vegetables and the portionsof plants with the preservatives described above.

For example, the treatment of vegetables such as broccoli with thepreservatives can delay yellowing of the vegetables.

The treatment of cut flowers such as carnation and rose can prolong thelife of flowers and can retard withering and wilting. Particularly, thetreatment of rose can delay flower opening which results in theprolonging of the life.

BRIEF DESCRIPTION OF DRAWING

FIGS. 1 and 2 show the changes of weights of cut flowers tested inExamples 8 and 9, respectively, against the number of days.

FIG. 3 is a figure wherein the change of the stage in the flower openingof cut rose flowers is expressed by numerical symbols, and

FIG. 4 shows the change of the stage in the flower opening of cutflowers tested in Example 11 against the number of days,

FIG. 5 shows the change of the weight % of cut flowers tested in Example11 water uptake,

FIG. 6 shows the change of the water uptake (g/cut flower weight-g) bycut flowers tested in Example 11 against the number of days,

FIG. 7 shows the change of the stage in the flower opening of cutflowers tested in Example 12 against the number of days,

FIG. 8 shows the change of weight % of cut flowers tested in Example 12against the number of days,

FIG. 9 shows the change of water uptake (g/cut flower weight-g) by cutflowers tested in Example 12 against the number of days,

FIG. 10 shows the change of the stage in the flower opening of cutflowers tested in Example 13 against the number of days,

FIG. 11 shows the change of the stage in the flower opening of cutflowers tested in Example 14 against the number of days, and

FIG. 12 shows the change of the weight % of cut flowers tested inExample 15 against the number of days.

FIG. 13 shows changes of the stage in the flower opening of cut flowerstested in the Example 15.

DETAILED DESCRIPTION OF THE INVENTION

The olefin compounds represented by the general formula (I) includecrotonic acid, propenyl-1-sulfonic acid, propenyl-1-phosphonic acid,propenylphenol, 2-butenylphosphonic acid, 1-butenylphosphonic acid,1-pentenylphosphonic acid, 1,2-diphosphonoethylene,propenyl-1,3-diphosphonic acid. These compounds include cis-form,trans-form and their mixture, and any of which can be used. Inparticular, cis-propenylphosphonic acid is preferred. There can be alsoused the alkali metal salts (sodium salts, potassium salts, etc.) oralkyl esters (methyl esters, ethyl esters, etc.) of the compoundsrepresented by the general formula (I).

The N-(2-chloro-4-pyridyl)ureas represented by the general formula (II)include N-(2-chloro-4-pyridyl)-N'-phenylurea,N-(2-chloro-4-pyridyl)-N'-(m-chlorophenyl)urea,N-(2-chloro-4-pyridyl)-N'-(o-methylphenyl)urea, etc. Particularly,N-(2-chloro-4-pyridyl)-N'-phenylurea is preferable.

Derivatives of dipicolinic acid wherein the positions of two carboxylgroups are different include pyridine-2,5-dicarboxylic acid, andpyridine-2,4-dicarboxylic acid. In addition, their alkali salts (sodiumsalts, potassium salts, etc.) can be used. Epoxy compounds representedby the general formula (III) include phosphomycin.

The SH-reagents include N-ethylmaleimide, p-chloromercuribenzoic acid,p-chloromercuribenzene sulfonic acid, iodoacetic acid, and5,5'-dithiobis (2-nitrobenzoic acid).

The preservative whose active ingredient(s) is a SH-reagent can beemployed for cut flowers in particular.

All of the above-described active ingredient(s) are known compounds, andare in the form of a solid at normal temperature under normal pressure.For example, cis-propenylphosphonic acid represented by the generalformula (I) is disclosed in JP-A-40,629/80 and in JP-A-52,299/83, andthe N-(2-chloro-4-pyridyl)ureas represented by the general formula (II)are disclosed in Japanese Patent Publication No. 16,104/82. Both thedipicolinic acid and the SH-reagents are commercially available as areagent.

These active ingredient(s) are employed in the form of a solution ofvarious concentrations. Each of the concentration is not particularlylimited since its optimum concentration differs depending on a type ofplants to which the preservation is to be applied.

The concentration of olefin compounds represented by the formula (I), orsalts thereof or esters thereof in a solution is in the range of 0.001to 5 weight %. It is preferred that the concentration used is in therange of 0.1 to 2 weight % for application to fruits and vegetables, and0.01 to 1 weight % for application to cut flowers. The usedconcentration of N-(2-chloro-4-pyridyl)ureas represented by the generalformula (II) in a solution is in the range of 0.01 to 50 ppm, preferably1 to 10 ppm for fruits and vegetables, and 0.1 to 10 ppm for cutflowers.

The concentration of dipicolinic acid or its derivatives used in asolution is in the range of 0.001 to 1 weight %, preferably 0.01 to 0.5weight %. The concentration of the epoxy compounds represented by thegeneral formula (III) and salts and esters thereof in the solution is inthe range of 0.001 to 5 weight %, preferably between 0.1 and 2 weight %for application to fruits and vegetables and between 0.01 and 1 weight %for application to cut flowers. The SH-reagent solution is used in therange of 1 to 1,000 ppm, preferably 5 to 50 ppm, in concentration.

The compounds can be used by being dissolved in a solvent, such aswater, alcohols, etc., that can dissolve the compounds. It is preferredthat they are used in the form of an aqueous solution.

As plants to which the preservatives of the present invention can beapplied, fruits and vegetables include cabbage, lettuce, broccoli,asparagus, spinach, beaN sprouts, burdock, spring chrysanthemum, corn,carrot, cauliflower, Brussels sprout, bamboo shoot, parsley, broad bean,celery, green pepper, turnip, tomato, eggplant, cucumber, mushrooms,champignon, kabosu (Citrus sphaerocarpa Tanaka), sudachi, apple, pear,tangerine, strawberry, peach, pineapple, banana, grape, melon, avocado,etc. and cut flowers and potted plants include carnation, sweetpea,gypsophila, gerbera, rose, chrysanthemum, lily, stock, statice, gentian,gladiolus, Turkish bellflower, tulip, orchid, etc.

The preservatives of the present invention are preferably employed inthe form of aqueous solution. The aqueous solution may be supplied tothe plants by any convenient method such as spraying, immersing ordrenching so long as the major portion of the plant.

A typical example of the treatment is immersion of the plant for onehour or more.

The preservatives of the present invention may also be used in powder orsolid form. The powder or solid can be scattered on the plant or can putinto a vase in which flowers are arranged.

The treatment of fruits or vegetables is usually carried out byimmersing the same in a liquid form of preservative for 1 to 20 hours.

In a range so as not to spoil effects of the above-described activeingredient(s), other known preservatives can be added therein asnecessary for use.

EXAMPLES Example 1 Effect of preservative on yellowing of broccoli

Commercial broccoli was cut into 5 to 10 g small pieces. With budsfacing down, 5 pieces were put in each of a 1 liter-beakers respectivelycontaining 200 ml each of a 0.1 weight % aqueous cis-propenylphosphonicacid solution (test group 1); a 1 weight % aqueouscis-propenylphosphonic acid solution (test group 2); and tap water(control group 1), followed by being immersed therein for 1 hour.

After the water was removed softly, the pieces in each group wereallowed to stand for 2 days in a 10-liter desiccater (a tray filled withwater was placed therein).

Then, change in the color of the buds was observed with naked eye. Inaddition, by measuring with colorimeter each lightness (L) and chroma ofthe broccoli (a: green to red, b: blue to yellow) before and after theywere allowed to stand, the difference in the color between before andafter being allowed to stand was calculated therefrom and regarded as ameasure of their green-fading and yellowing. (The higher ΔE indicatesthe progress of green-fading and yellowing. However, since the value isaffected by lightness and chroma of plants before the test, it isregarded as a measure of change in the color of the buds for the Exampleonly.)

    ΔE={(ΔL).sup.2 +(Δb).sup.2 +(Δb).sup.2 }

ΔE; difference in the color of the broccoli buds between before andafter being allowed to stand

ΔL; difference in the "L" value between before and after being allowedto stand

Δa; difference in the "a" value between before and after being allowedto stand

Δb; difference in the "b" value between before and after being allowedto stand.

Results are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                        Test group and control                                                                         After 2 days                                                 group            Appearance    ΔE*                                      ______________________________________                                        Test group 1     Yellowing to some                                                                           6.3 ± 0.8                                   a 0.1 weight % aqueous                                                                         extent                                                       cis-propenylphosphonic                                                        acid solution                                                                 Test group 2     Little yellowing                                                                            4.5 ± 1.0                                   an 1 weight % aqueous                                                                          Keeping green                                                cis-propenylphosphonic                                                                         considerably                                                 acid solution                                                                 Control 1        Complete yellowing                                                                          9.0 ± 1.8                                   Tap water                                                                     ______________________________________                                         *Average ± Standard Deviation                                         

Example 2 Effect of preservative on yellowing of broccoli

The procedure was carried out in the same manner as in Example 1 exceptfor the uses, as test groups, of an 1 ppm aqueousN-(2-chloro-4-pyridyl)-N'-phenylurea solution (test group 1) and a 10ppm aqueous N-(2-chloro-4-pyridyl)-N'-phenylurea solution (test group 2)and, as control groups, of an 1 ppm aqueous 6-benzyladenine solution(control group 1), a 10 ppm aqueous 6-benzyladenine solution (controlgroup 2), an 1 ppm aqueous kinetin solution (control group 3), a 10 ppmaqueous kinetin solution (control group 4), and tap water (control group5).

Results are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                        Test group and control                                                                       After 2 days                                                   group          Appearance      ΔE*                                      ______________________________________                                        Test group 1   No yellowing    1.3 ± 0.3                                   an 1 ppm aqueous N-(2-                                                                       Keeping green perfectly                                        chloro-4-pyridyl)-                                                            N'-phenylurea solution                                                        Test group 2   No Yellowing    1.1 ± 0.7                                   an 10 ppm aqueous N-                                                                         Keeping green perfectly                                        (2-chloro-4-pyridyl)-                                                         N'-phenylurea solution                                                        Control 1      Yellowing to some                                                                             3.6 ± 2.2                                   an 1 ppm aqueous                                                                             extent                                                         6-benzyladenine                                                                              Green-fading to some                                           solution       extent                                                         Control 2      Yellowing to some                                                                             2.7 ± 1.0                                   a 10 ppm aqueous                                                                             extent                                                         6-benzyladenine                                                                              A little green-fading                                          solution                                                                      Control 3      A little yellowing                                                                            4.2 ± 1.2                                   an 1 ppm aqueous                                                                             Green-fading to some                                           kinetin solution                                                                             extent                                                         Control 4      A little yellowing                                                                            3.4 ± 0.8                                   a 10 ppm aqueous                                                                             Green-fading to some                                           kinetin solution                                                                             extent                                                         Control 5      Complete yellowing                                                                            10.3 ± 1.7                                  Tap water                                                                     ______________________________________                                         *Average ± Standard Deviation                                         

EXAMPLE 3 Effect of preservative on yellowing of broccoli

The procedure was carried out in the same manner as in Example 1 exceptfor the use, as test groups, of a 0.02 weight % aqueous dipicolinic acidsolution (test solution (test and a 0.2 weight % aqueous dipicolinicacid solution (test group 2).

Results are shown in Table 3.

                  TABLE 3                                                         ______________________________________                                        Test group and control                                                                         After 2 days                                                 group            Appearance    ΔE*                                      ______________________________________                                        Test group 1     Yellowing to some                                                                           6.5 ± 1.2                                   a 0.02 weight %  extent                                                       aqueous dipicolinic                                                           acid solution                                                                 Test group 2     Little yellowing                                                                            4.8 ± 0.6                                   a 0.2 weight % aqueous                                                                         Keeping green                                                dipicolinic acid considerably                                                 solution                                                                      Control 1        Complete yellowing                                                                          9.2 ± 1.5                                   Tap water                                                                     ______________________________________                                         *Average ± Standard Deviation                                         

Example 4 Preventive effect on withering of cut carnation flower

Carnations (Dianthuscaryophyllus L. cv. Coral) were cut in water to alengths of 30 cm, immediately after harvest. The stems of the nineflowers were immersed, in each of a 200-ml Erlenmeyer flasksrespectively containing 100 ml each of a 0.01 weight % aqueouscis-propenylphosphonic acid solution (test group 1); a 0.1 weight %aqueous cis-propenylphosphonic acid solution (test group 2); and tapwater (control group 1). Then, they were allowed to stand at roomtemperature, and the degree of their withering was observed with thenaked eye daily. Results are shown in Table 4. (Since the results areaffected by some conditions, such as harvesting time of plants examinedbefore the test, the degree of the withering progress is regarded as ameasure for the Example only.)

                  TABLE 4                                                         ______________________________________                                                          Days                                                        Test group and control group                                                                      0     4     8   12   16                                   ______________________________________                                        Test group 1        -     -     -   -    +                                    a 0.01 weight % aqueous                                                       cis-propenyl-phosphonic acid solution                                         Test group 2        -     -     -   -    -                                    a 0.1 weight % aqueous cis-propenyl-                                          phosphonic acid solution                                                      Control group 1     -     ±  +   ++   +++                                  tap water                                                                     ______________________________________                                         -: No withering,                                                              ±: Start of a little withering,                                            +: Obvious withering,                                                         ++: Almost complete withering,                                                +++: Putrefaction in addition to withering                               

Example 5 Preventive effect on withering of cut carnation flowers

Respective 5 carnations were treated in the same manner as in Example 4except for the use, as test groups, of a 0.1 ppm aqueousN-(2-chloro-4-pyridyl)-N'-phenylurea solution (test group 1), an 1 ppmaqueous N-(2-chloro-4-pyridyl)-N'-phenylurea solution (test group 2),and an 1 ppm aqueous N-(2-chloro-4-pyridyl)-N'-(m-chloro-phenyl)ureasolution (test group 3), and, as control groups, of an 1 ppm aqueous6-benzyladenine solution (control group 1), an 1 ppm aqueous kinetinsolution (control group 2), and tap water (control group 3).

Results are shown in Table 5.

                  TABLE 5                                                         ______________________________________                                                          Days                                                        Test group and control group                                                                      0     2     4   6    8                                    ______________________________________                                        Test group 1        -     -     -   -    -                                    a 0.1 ppm aqueous                                                             N-(2-chloro-4-pyridyl)-N'-                                                    phenylurea solution                                                           Test group 2        -     -     -   -    ±                                 an 1 ppm aqueous                                                              N-(2-chloro-4-pyridyl)-N'-                                                    phenylurea solution                                                           Test group 3        -     -     -   -    +                                    an 1 ppm aqueous                                                              N-(2-chloro-4-pyridyl)-N'-                                                    (m-chloro-phenyl)urea solution                                                Control group 1     -     -     -   ± ++                                   an 1 ppm aqueous 6-benzyladenine                                              solution                                                                      Control group 2     -     -     -   +    ++                                   an 1 ppm aqueous kinetin solution                                             Control group 3     -     ±  +   ++   +++                                  Tap water                                                                     ______________________________________                                         -: No withering,                                                              ±: Start of a little withering,                                            +: Obvious withering,                                                         ++: Almost complete withering,                                                +++: Putrefaction in addition to withering                               

Example 6 Preventive effect on withering of cut carnation flowers

The procedure was carried out in the same manner as in Example 4 exceptfor the use, as test groups, of a 0.2 weight % aqueous dipicolinic acidsolution (test group 1), a 0.2 weight % aqueouspyridine-2,5-dicarboxylic acid solution (test group 2), and a 0.2 weight% aqueous pyridine-2,4-dicarboxylic acid solution (test group 3).

Results are shown in Table 6.

                  TABLE 6                                                         ______________________________________                                                          Days                                                        Test group and control group                                                                      0     2     4   6    8                                    ______________________________________                                        Test group 1        -     -     -   -    -                                    a 0.2 weight % aqueous dipicolinic                                            acid solution                                                                 Test group 2        -     -     -   ± +                                    a 0.2 weight % aqueous pyridine-2,5-                                          dicarboxylic acid solution                                                    Test group 3        -     -     -   +    ++                                   a 0.2 weight % aqueous pyridine-2,4-                                          dicarboxylic acid solution                                                    Control group 1     -     ±  +   ++   +++                                  Tap water                                                                     ______________________________________                                         -: No withering,                                                              ±: Start of little withering,                                              +: Obvious withering,                                                         ++: Almost complete withering,                                                +++: Putrefaction in addition to withering                               

Example 7 Preventive effect on withering of cut carnation flowers

The tests were carried out in the same manner as in Example 4 except forthe use, as test groups, of a 10 ppm aqueous N-ethylmaleimide solution(test group 1), a 10 ppm aqueous p-chloromercuribenzene sulfonic acidsolution (test group 2), and a 10 ppm aqueous iodoacetic acid solution(test group 3).

Results are shown in Table 7.

                  TABLE 7                                                         ______________________________________                                                          Days                                                        Test group and control group                                                                      0     4     8   12   16                                   ______________________________________                                        Test group 1        -     -     -   -    -                                    a 10 ppm aqueous N-ethylmaleimide                                             solution                                                                      Test group 2        -     -     -   -    ±                                 a 10 ppm aqueous p-chloromercuri-                                             benzene                                                                       sulfonic acid solution                                                        Test group 3        -     -     -   -    +                                    a 10 ppm aqueous iodoacetic acid                                              solution                                                                      Control group 1     -     ±  +   ++   +++                                  Tap water                                                                     ______________________________________                                         -: No withering,                                                              ±: Start of a little withering,                                            +: Obvious withering,                                                         ++: Almost complete withering,                                                +++: Putrefaction in addition to withering                               

Example 8 Preventive effect on withering of cut carnation flowers

Carnations (Dianthus caryophyllus L. cv. Coral) were cut in water tolengths of 30 cm, immediately after harvest. Then each cut flower wasput in each of a 61 ml-test tubes respectively containing 30 ml each ofan aqueous mixture solution of 1 weight % cis-propenylphosphonic acid,0.2 weight % dipicolinic acid, and 10 weight % sucrose (test group 1),tap water (control group 1), and an aqueous solution of silverthiosulfate (0.1 mmol/l, control group 2) which is known to demonstratea significant effect on delay withering of carnation, and the stem wasimmersed therein for 3 hours. Six cut flowers were used for one testgroup, respectively.

Then, all of the cut flowers were taken out from the respectiveimmersing solutions, and the each flower was transferred to 61 ml-testtube containing 30 ml of tap water in each, and the flower was allowedto stand at room temperature. The degree of withering was observed withthe naked eye daily, and the weight of the cut flowers was alsomeasured.

Results are shown in Table 8 and FIG. 1.

                  TABLE 8                                                         ______________________________________                                                           Vase life; the days                                                           until withering starts                                                        (mean of 6 flowers ±                                    Test group and control group                                                                     standard deviation)                                        ______________________________________                                        Test group 1       11.7 ± 0.5                                              1 weight % cis-propenyl-                                                      phosphonic acid                                                               0.2 weight % dipicolinic acid                                                 10 weight % sucrose                                                           Control group 1     6.3 ± 0.5                                              Tap water                                                                     Control group 2    11.2 ± 1.5                                              a silver thiosulfate solution                                                 (0.1 mmol/l)                                                                  ______________________________________                                    

Example 9 Preventive effect on withering of cut carnation flowers

The procedure was carried out in the same manner as in Example 8 exceptfor the use of "Yukon" as a cultivar of carnation.

Results are shown in Table 9 and FIG. 2.

                  TABLE 9                                                         ______________________________________                                                           Vase life; the days                                                           until withering starts                                                        (mean of 6 flowers ±                                    Test group and control group                                                                     standard deviation)                                        ______________________________________                                        Test group 1       12.7 ± 0.8                                              weight % cis-propenyl-                                                        phosphonic acid                                                               0.2 weight % dipicolinic acid                                                 10 weight % sucrose                                                           Control group 1     7.2 ± 1.0                                              Tap water                                                                     Control group 2    12.7 ± 2.1                                              a silver thiosulfate solution                                                 (0.1 mmol/l)                                                                  ______________________________________                                    

Example 10 Preventive effect on withering of cut carnation flowers

The procedure was carried out in the same manner as in the Example 8except for the use of "Arisetta" of a spray type as a cultivar ofcarnation and for the use, as test groups, of an aqueous mixturesolution of 0.5 weight % cis-propenylphosphonic acid, 0.1 weight %dipicolinic acid, and 10 weight % sucrose and, as a control group, oftap water.

Results are shown in Table 10.

                  TABLE 10                                                        ______________________________________                                                           Vase life; the days                                                           until withering starts                                                        (mean of 6 flowers ±                                    Test group and control group                                                                     standard deviation)                                        ______________________________________                                        Test group 1       13.4 ± 2.6                                              0.5 weight % cis-propenyl-                                                    phosphonic acid                                                               0.1 weight % dipicolinic acid                                                 10 weight % sucrose                                                           Control group       7.0 ± 1.3                                              Tap water                                                                     ______________________________________                                    

Example 11 Effect on prolonging the life of cut roses

Roses (Rosa hibrida L. cv. Sonia) were cut in water to lengths of 30 cm,immediately after harvested in the state of bud. The each cut flower wasput in each of a 61 ml-test tubes respectively containing 30 ml each ofa 0.01 weight % aqueous cis-propenylphosphonic acid solution (test group1); an aqueous mixture solution of 0.01 weight % cis-propenylphosphonicacid and 3 weight % sucrose (test group 2), tap water (control group 1)and a commercial preservative for cut flower (a vase treatment agent"Hana no Sei" (Flower Sprite) made by Palace Chemical Corp., controlgroup 2), to immerse its stem therein.

Then, they were allowed to stand in a room where the temperature and therelative humidity were adjusted to 20° C., 70%, respectively, and thestage in the flower opening and the external appearance of the flowerswere observed with the naked eye daily. In addition, weight of the cutflowers as well as water uptake were measured.

The stage in the flower opening, as shown in FIG. 3, is expressed asnumerical symbols, from the stage of the bud. The number in FIG. 3indicates the stage in the flower opening. In the drawings, *1 meansthat the flower opened too much (including an exposed style of theflower), and *2 means that the flower opened too much more than stage 7.

As for the effect on prolonging the life of flower, flowers were judgedto lose their ornamental values (the end point of flower) when two ormore of five cut flowers tested showed their flowers apparently openedtoo much (including an exposed style of the flower), dropped of petals,withered, or drooped or a hamful effect of the chemical was shown, andthen the observation and measurements were stopped.

Results are shown in FIGS. 4, 5, and 6. The data in the figures in thedrawing show mean values of five cut flowers.

Example 12 Effect on prolonging the life of cut roses

Roses (Rosa hibrida L. cv. Sonia) were cut in water to lengths of 30 cm,immediately after harvested in the state of bud. Then each cut flowerwas put in each of a 61 ml-test tubes respectively containing 30 ml eachof a 0.01 weight % aqueous cis-propenylphosphonic acid solution (testgroup 1); a 0.05 weight % aqueous cis-propenylphosphonic acid solution(test group 2); or an aqueous mixture solution of 0.05 weight %cis-propenylphosphonic acid and 5 weight % sucrose (test group 3); andtap water (control group) to immerse the stem of the respective flowersfor 20 hours therein.

Five cut flowers were employed for each of the test group. Then, all ofthe cut flowers were taken out from the each immersing solution, andthen each flower was transferred to a 61 ml-test tube containing 30 mlof tap water, to immerse the stem, and was measured for the same itemsas in Example 11.

The above procedures were carried out in a room where the temperatureand the relative humidity were adjusted to 20° C. and 70%, respectively.

Results are shown in FIGS. 7, 8, and 9. The data shown in FIGS. indicatemean values.

Example 13 Effect on prolonging the life of cut roses

Carina (Rosa hibrida L.) was employed as a cultivar of rose flower. Theprocedure was carried out in the same manner as in Example 12 except forthe use of a 0.01 weight % aqueous cis-propenylphosphonic acid solution(test group 1), a 0.05 weight % aqueous cis-propenylphosphonic acidsolution (test group 2), and tap water (control group 1) and theprocedure was carried out in the same manner as in Example 11 except forthe use of a commercial preservative [a vase treatment agent "Hana noSei" (Flower Sprite), as control group 2].

Results are shown in FIG. 10. The data in the figure indicate meanvalues of five cut flowers.

Example 14 Effect on prolonging the life of cut roses

The procedure was carried out in the same manner as in Example 11 exceptfor the use, as a test group, of a 0.05 weight % aqueouscis-propenylphosphonic acid solution (test group 1), and the use, ascontrol groups, of tap water (control group 1), a 0.01 weight % aqueouspropenylphosphonic acid solution (control group 2), and a 0.05 weight %aqueous phenylphosphonic acid solution (control 3).

Results are shown in FIGS. 11 and 12. The data indicated in the figuresare mean values of five cut flowers.

Example 15 Effect on prolonging the life of cut roses

The procedure was carried out in the same manner as in Example 12 exceptfor the use, as a test group, of 0.1 weight % aqueous solution ofphosphomycin sodium salt (test group 1) and of 0.2 weight % aqueoussolution of sodium salt of phosphomycin (test group 2).

Results are shown in FIG. 13. The data indicated in the figure are meansvalue of five cut flowers.

Example 16 Preventive effect on withering of cut carnation flowers

The procedure was carried out in the same manner as in Example 4 exceptfor the use, as a test group, of 0.4 weight % aqueous solution ofphosphomycin sodium salt solution, and, as control groups, of tap water(control group 1) and of 0.4 weight % aqueous phenylphosphonic acidsolution (control group 2). Results are shown in Table 11.

                  TABLE 11                                                        ______________________________________                                                            Days                                                      Test group and control group                                                                        0     2     4   6   8                                   ______________________________________                                        Test group            -     -     -   -   ±                                0.4 weight % aqueous phosphymycin                                             sodium salt solution                                                          Control group 1       -     -     +   +   ++                                  Tap water                                                                     Control group 2       -     -     +   +   ++                                  0.4 weight % aqueous phenylphosphonic                                         acid solution                                                                 ______________________________________                                         -: No withering,                                                              ±: Start of a little withering,                                            +: Obvious withering                                                          ++: Almost complete withering                                            

Example 17 Extended effect on vase life of cut tulip flowers

Commercially available tulip (type: pink supreme) was cut in water tolengths of into a 50 cm flower in length in water. Then each cut flowerwas put in each of a 61 ml-test tube respectively containing 30 ml eachof an aqueous mixture solution of 0.1 weight % cis-propenylphosphonicacid (test group) and a tap water (control group). Three cut flowerswere used for both the test group and the control group.

Thereafter all the cut flowers were allowed to stand in the same roomwith temperature and the relative humidity controlled at 20° C. and 70%respectively, and the appearance of each cut flower (petals, stems,etc.) was observed with the naked eye every day.

Results are shown in Table 12.

                  TABLE 12                                                        ______________________________________                                        Test group                                                                    and control                                                                           Days                                                                  group   0        2        4      6      8                                     ______________________________________                                        Test group                                                                            Normal   Normal   Normal Normal Normal                                0.1 weight                                                                    % aqueous                                                                     cis-pro-                                                                      penylphos-                                                                    phonic acid                                                                   solution                                                                      Control Normal   Normal   A bit  Bowing -*                                    group                     bowing of stems,                                    Tap water                 of stems                                                                             fallen                                                                        petals                                       ______________________________________                                         -*: Measurement ended at the sixth day, therefore no results are              available.                                                               

What is claimed is:
 1. A method for maintaining the freshness of aharvested plant or plant part which comprises treating the plant orplant part with a preservative containing dipicolinic acid or aderivative or salt thereof.
 2. The method according to claim 1, whereinthe plant or plant part is a fruit, a vegetable, a leaf, a branch, aflower, a root or a stem.
 3. The method according to claim 1, whereinsaid harvested plant or plant part is a plant or plant part that hasbeen severed from its natural growing environment and in which thesevered plant or plant part is treated by contacting the severed portionthereof with said preservative.
 4. The method according to claim 1,wherein said derivative of dipicolinic acid is pyridine-2,4-dicarboxylicacid or pyridine-2,5-dicarboxylic acid.
 5. The method according to claim1, where said plant is broccoli.
 6. The method according to claim 3,wherein said plant part is a cut flower.
 7. The method according toclaim 6, in which the cut flower is a carnation.